Subcutaneous birch pollen allergen immunotherapy with a depigmented polymerized extract shows only sustained and long‐term efficacy in a subgroup of monosensitized adults and adolescents with allergic rhinitis

Abstract Background Allergen immunotherapy (AIT) is an approved treatment for seasonal respiratory allergic diseases. A depigmented polymerized birch pollen extract for subcutaneous allergen immunotherapy (SCIT) has been demonstrated to be efficacious and safe in patients allergic to birch pollen and its homologous group. Objective To determine whether SCIT with a birch pollen formulation (5000 depigmented polymerized (DPP) units/mL) shows sustained and long‐term efficacy in adults and adolescents with birch‐pollen induced allergic rhinitis with or without intermittent asthma. Methods A multicentre (n = 66), double‐blind, placebo‐controlled Phase III clinical trial was performed in the Czech Republic, Finland, Germany, Latvia, Lithuania, Poland and Russia. Participants were randomized 2:1 to active treatment (birch 5000 DPP/ml) or placebo for three years of SCIT and followed up for two treatment‐free years. The primary efficacy endpoint was the EAACI's combined symptom and medication score for rhinoconjunctivitis (CSMSEAACI). Results A total of 973 participants were screened and 649 were randomized (active treatment: n = 434; placebo: n = 215). The intention‐to‐treat analysis of the CSMSEAACI in the overall study population did not demonstrate statistically significant differences in years 1, 2 and 3. In a post‐hoc analysis, among the subgroup of patients monosensitized to birch pollen allergen only (n = 200), we observed a statistically significant difference (active treatment vs. placebo) in the CSMSEAACI in year 2, 3 and 5. The AIT's safety profile was good. Conclusions SCIT with a depigmented polymerized birch pollen extract was safe. Sustained and long‐term efficacy in years 2, 3 and 5 in monosensitized patients, but not in polysensitized patients was demonstrated. (EudraCT 2012‐000414‐11)

1 birch pollen allergen may trigger oral allergy syndrome in up to 70% of birch-pollen-allergic patients. 14,15 The symptoms of birch pollen AR can be relieved (at least temporarily) with symptomatic medications, including H1 antihistamines, leukotriene receptor antagonists, and corticosteroids. [16][17][18] However, these medications may lack efficacy or be poorly tolerated. The only currently available, systemic, diseasemodifying treatment for allergic respiratory diseases is allergen immunotherapy (AIT). 19,20 By acting directly on the immune system, AIT induces tolerance to the disease-inducing allergen. [21][22][23] After over a century of clinical use and the development of modern pharmaceutical formulations over the last decades, both subcutaneous allergen immunotherapy (SCIT) or sublingual allergen immunotherapy (SLIT) have proven their efficacy and safety in the treatment of AR and/or AA induced by a range of allergens, including pollens. 18,[23][24][25][26][27][28][29][30][31][32][33] A variety of pharmaceutical formulations of birch pollen extracts have been marketed for SCIT or SLIT in patients with moderate-to-severe birch pollen allergy. [34][35][36] One such formulation is depigmented polymerized birch SCIT, which has been marketed as a named patient preparation at doses of up to 1000 DPP/mL (corresponding to ∼7 μg Bet v 1/mL prior to depigmentation) in Spain and Germany. 34,37,38 The results of a dose-ranging study (EudraCT 2008-008448-26, NCT01144429) of 100, 1000, 5000 and 10,000 DPP/mL formulations suggested that the 5000 DPP/mL dose level had an even more favourable efficacy and a comparable safety profile to the 1000 DPP/mL dose level. 39 The present study constituted part of the Phase III clinical development of this 5000 DPP/mL formulation (EudraCT 2012-000414-11).
As mentioned above, the mode of action of AIT is based on longterm tolerance of disease-inducing allergens. Currently, regulatory authorities take account of the time scale of efficacy for AIT products. The European Medicines Agency (EMA) recommends that AIT preparations have (i) short-term efficacy (i.e. in the first season or year of treatment), (ii) sustained efficacy (i.e. the maintenance of efficacy for two to three seasons or years), and (iii) long-term efficacy (following the withdrawal of treatment). 40 Most guidelines recommend a 3-year course of AIT, and this duration is supported by data from the literature. 27 Hence, the overall goal of this multinational, multicentre, double-blind, placebo-controlled (DBPC) randomized clinical trial with two parallel groups was to demonstrate the clinical efficacy of a birch 5000 DPP/mL SCIT preparation (vs. placebo) during 3 years of treatment and two post-treatment years 25,26,41 in adults and adolescents with birch pollen AR (with or without intermittent asthma).
The primary objective of the present study was therefore to test the superiority of active treatment with regard to a combined symptom and medication score (CSMS). The secondary objectives were to establish the active treatment's efficacy with regard to other endpoints (including symptom scores, a rescue medication (RM) score, disease-specific quality of life, and immunological parameters) and to assess local and systemic safety and tolerability.

| Trial design
We performed a Phase III multinational, multicentre, DBPC randomized clinical trial with two parallel groups. The study centres were located in the Czech Republic, Finland, Germany, Latvia, Lithuania, Poland, and Russia. There were two recruitment periods: the first ran from September 2012 to January 2013, and the second started after the end of the 2013 birch pollen season (August 2013) and continued until January 2014. After a screening phase, eligible patients were randomized to active treatment (see below) or placebo.
The study comprised an 8-week screening phase, a 1-day initial buildup phase, a blinded 3-year maintenance treatment phase (including three birch pollen seasons, with treatment administered monthly) and a 2-year blinded, treatment-free follow-up phase (including 2 birch pollen seasons). The total study duration per patient was approximately 5 years.
Start-and end-dates of local pollen seasons were determined by local pollen exposure reports for each study centre. The start date of relevant birch pollen exposure was defined as the first of three consecutive days with a pollen count ≥50 grains/m 3 /24 h. 38 The end date of the birch pollen season was defined as the day one week after the last day of the year with ≥50 pollen grains/m 3 /24 h.

| Trial population
The study's main inclusion criteria were as follows: (i) age from 12 to 70 at the time of screening; (ii) a physician-documented history of at least 2 years of treated seasonal AR with or without intermittent asthma; (iii) self-rated, moderate-to-severe symptoms in at least the two previous birch pollen seasons; (iv) peak expiratory flow ≥80% predicted; (v) IgE-mediated sensitization to birch pollen allergen, as defined by a suggestive medical history, serum specific IgEs (sIgEs) to birch pollen and a positive (wheal diameter ≥3 mm) skin prick test

| Randomization
Included patients were assigned a unique identifier (a 3-digit site number, followed by an increasing 3-digit patient number) before randomization 2:1 to active treatment or placebo. The randomization schedule was generated by a clinical research organization using dedicated software and was not known to the investigators or other study personnel. Copies of the randomization schedule were provided to (i) LETI Pharma (Tres Cantos, Spain) for supply of the active treatment, and (ii) a clinical trial supplies and services provider responsible for the distribution of the active treatment and noninvestigational medical products and for ad hoc substitution of active treatment kits in the event of damage (e.g. freezing). For emergency un-blinding, the investigational sites received sealed code cards corresponding to the active treatment kit numbers they had received for their patients.

| Study treatments
The active treatment for SCIT was Birch 5000 DPP/mL (LETI Pharma), a depigmented polymerized allergen extract adsorbed onto aluminium hydroxide and suspended in 0.9% NaCl with 0.5% phenol.
The DPP unit corresponds to the depigmentation and polymerization of 1 histamine equivalent (in an SPT) in the allergenic extract. The histamine equivalent unit was 10 mg/ml. The 5000 DPP/mL dose corresponds to a titre of ∼35 μg Bet v1/mL prior to depigmentation.
To maintain blinding, the placebo SCIT formulation had the same appearance as the active treatment. The treatment regimen comprised a rush build-up phase (two separate injections-0.2 and 0.3 mL-administered 30 min apart on day 1) and a maintenance phase (one 0.5 mL injection per visit at 4-to 6-week intervals for up to 36 months, giving a total of up to 29 maintenance injections).

| Endpoints and assessments
The initially specified primary efficacy variable was a CSMS that Lastly, the intensity of each AE was rated as mild (tolerable), moderate (bothersome, interference with usual activities) or severe (inability to perform usual activities).
In order to investigate potential confounder variables and their possible impact on the treatment effect of birch 5000 DPP/mL versus placebo, an explorative post-hoc confounder analysis was performed.

| Sample size calculation and statistical analysis
The sample size calculation was based on the sponsor's previous clinical studies in this indication, with the following assumptions: an NOVAK ET AL.

| Ethics
All participants aged 18 or over gave their written consent to participation, after having been informed of the study's objectives and procedures. Participants aged 12 to 17 gave their assent to participation, and the participants' parents or legal representatives gave their written consent. The study was approved by the appropriate independent ethics committees in each country and was registered in the European Clinical Trials Database (EudraCT 2012-000414-11).

| Primary endpoint
The post-hoc analysis of the primary endpoint (CSMS EAACI ) (which was changed from CMCS 0-36 during the study as already  Table 2). Similarly, a statistically significant active treatment versus placebo difference was also found for the median CSMS lung in year 3 (p = 0.0057) and year 5 (p = 0.0489) ( Table 2)

| Secondary endpoints (in monosensitized patients)
An analysis of the median total symptom score demonstrated a statistically significant difference in favour of active treatment (23.8% lower than placebo) at the end of the treatment phase only (year 3, p = 0.0342). The median RMS was low in both treatment groups, indicating that RMs were rarely used by the study patients. However, there were statistically significant differences in favour of the active treatment in years 3 and 5 (62.5% lower than placebo, p = 0.00013, and 57.1% lower than placebo, p = 0.0032, respectively; Table 3).
Like-wise, the median integrated RMS for asthmatic patients was  increased faster over time in the active treatment group than in the placebo group, although the differences were not statistically significant ( Table 3). The mean number of hell days decreased over time in the active treatment group and was stable over time in the placebo group; at the end of the treatment period, the difference was statistically significant (p = 0.0019).
With regard to immunological variables for mono-sensitized patients, the mean titre of birch-pollen-specific IgE was lower in the active treatment group than in the placebo group in year 3 and year 5, while the mean titre of birch-pollen-specific IgG4 was higher in the active treatment group than in the placebo group in year 3 and year 5 (Table 3 and Figure 3).    Table 6). The frequency of TEAEs was similar across all patient sets.

| Safety
The overall assessment of the active treatment's tolerability was "excellent" or "good" in 91.6% of patients (according to the investigator) or in 87% (according to the patients themselves).
With regard to patients with asthma, the vast majority in both treatment groups reported no changes or even an improvement in their asthma status during the study.

| DISCUSSION
The present study is the first birch pollen SCIT trial to be designed in line with the EMA's guidance on demonstrating short-term, sustained and long-term efficacy in the clinical development of AIT products. 40 The study's objective was thus to highlight the long-term efficacy and Parietaria officinalis)) pollen SCIT. 48 Hence, the present trial of birch pollen SCIT now joins this list.
The present study's objective of long-term efficacy was not met for the study population as a whole: an interim analysis did not yield statistically significant results for the primary endpoint in the whole  Confounder analyses revealed stronger effect of birch pollen SCIT in mono-sensitized patients with higher symptom score at onset of the study and larger birch pollen skin prick test wheal diameter.
Also a trend could be observed for BMI with a reduced treatment effect in patients with higher BMI.
Our study addresses a longstanding question: the efficacy of specific AIT in polysensitized patients. One hypothesis, which can be drawn from the data is that allergen immunotherapy especially SCIT is only effective if the Th2 dominance is not sustained, or vice versa it is not effective in Th2-athletes who are polysensitized and may have high total IgE and eosinophils. A major result is that monosensitized patients will profit most, prompting the need for detailed molecular IgE diagnosis.
So far it is unclear, why other studies, in particular SLIT studies which used comparable exclusion criteria for example, history of potentially confounding symptoms triggered by allergens other than birch pollen (grass pollen, weed pollen, house dust mites, and cat or dog dander) reached significant differences even in the group of polysensitized patients.
The study had some limitations-several of which are inherent to placebo-controlled studies of AIT in which participants are exposed to confounding allergens. 50 Firstly, and as mentioned above, a high proportion of the patients were mono-allergic but polysensitized; this might have masked (at least partially) active treatment versus placebo differences. Nevertheless, significant efficacy was seen in the subset of monosensitized, mono-allergic participants. Secondly, and as also mentioned above, patient recruitment took place over two successive pollen seasons; this introduced a potential source of bias.
Thirdly, the recruitment target for adolescent study participants was not met, which prevented a quantitative assessment of the treatment effect in this subgroup.
This was the first long-term DBPC study of birch pollen SCIT.
Large DBPC studies with long-term follow-up are complex and expensive to perform; however, they provide a lot of important information on study designs, quality criteria and scores and, ultimately, improve the management of allergic patients in clinical practice. 33,51 Even when these long-time studies' primary endpoints are not met (e.g. as in the scientifically informative GAP trial 52 ), they provide much additional information via (for example) analyses of secondary endpoints or post-hoc analyses; their results must be published for ethical and practical reasons.
In conclusion, treatment with Birch 5000 DPP in an indication of birch-pollen induced AR with or without asthma showed efficacy after 3 years of treatment and long-term efficacy (compared with placebo) in year 5 in the subset of patients (monosensitized, mono-allergic individuals). The safety profile was consistent with the literature data accumulated using different doses of birch SCIT formulations.